STABILIZING THE ABUTMENT OF DEADWOOD ARCH DAM

摘要

A large continuous joint plane cuts through the left abutment of Dead wood Dam, forming a readily apparent block that underlies the dam. Drilling and mapping efforts indicated that an additional joint plane on the downslope side and a joint set parallel to the upstream face of the dam, combined with the prominent base plane to form block intersections that "daylight" downstream. Piezometers provided estimates of foundation water pressures, and field observations along with laboratory direct shear tests provided estimates of the joint friction angles. Dam loads were calculated from three-dimensional finite element analyses. Sliding factors of safety less than 1.0 and several inches of permanent displacement were calculated under the design earthquake ground motions. Based on the analyses, the risks were estimated to exceed Reclamation's public protection guidelines, and corrective actions were initiated. This included installation of drainage and fully grouted high strength rock bolts to keep the sliding factors of safety above 1.0 for the design earthquake. Due to the steep topography and difficult access, the rock bolt installation was successfully accomplished by helicopter.